Freezing tunnel cold-gas extraction hoods with variable-opening extractors

ABSTRACT

An installation for cryogenic cooling or freezing of products includes: a cryogenic tunnel through which products that are to be cooled or frozen circulate, between an entrance into the tunnel and an exit from the tunnel on a conveyor belt; an upstream extraction hood situated facing the entrance to the tunnel and/or a downstream extraction hood situated facing the exit from the tunnel; and movable blinds or shutters that make it possible to close all or part of a suction cross section of at least one of the said hoods over a width and depth of the conveyor belt.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a § 371 of International PCT Application PCT/FR2018/050691, filed Mar. 22, 2018, which claims § 119(a) foreign priority to French patent application FR 1752572, filed Mar. 28, 2017.

BACKGROUND Field of the Invention

The present invention relates to the field of the extraction hoods with which deep-freezing tunnels are equipped.

Related Art

Deep-freezing tunnels are usually equipped with two hoods for extracting the cold gases from the top of the area housing the tunnels: one at the tunnel entrance, and one at the tunnel exit, and which serve to optimize the removal, from the area, of the gases resulting from the vaporization of the cryogenic fluids used in the tunnel (usually nitrogen or CO₂). This extraction system therefore has the role of removing the gases formed in the apparatus and thus of ensuring the safety of the operators by protecting them from any risk of anoxia, while at the same time maintaining the productivity of the tunnels.

Nevertheless, it should be noted that while the tunnels are usually fitted with two extraction hoods, it does sometimes happen that tunnels are equipped with just one hood, or that tunnels are operated with just one of their two hoods in operation, usually the one situated at the entrance.

The cross section of these hoods is traditionally rectangular in shape, having the same width as the tunnel conveyor.

The extraction flow rate of each of these hoods needs to be correctly adjusted so as to extract just the right amount of gas, i.e. to extract enough gas to prevent gases from spreading out of the tunnel and endangering the operators, but without performing excessive extraction, so as not to extract the cold gases from the tunnel to the outside and thus lead to an overconsumption of cryogenic fluid.

In general, the starting point is to try to contain the fluid in the middle of the tunnel using curtains or deflectors; the cold gases in the tunnel are then balanced using deflectors or fans referred to as “circulators” and then the extraction flow rate is adjusted.

At the present time, if it is found that gas is spreading toward the outside at the open parts of the tunnel, at the entrance and/or the exit, the extraction flow rate is increased.

Now, there are instances in which the leakage of cold gas is more significant on one side of the hood than on the other. For example, the gases may have a tendency to escape via the left-hand part of the hood. This state of affairs (leaking gas) is easily diagnosed, for example from measurements of oxygen content and/or from temperature measurements, which point toward an oxygen-poor (<14%) atmosphere and a very low (<0° C.) temperature.

The response currently adopted to remedy this situation is to increase the overall extraction flow rate (extraction flow rate on the left-hand part but also on the right-hand part) and therefore to extract more cold gas across the entire width of the tunnel belt from right to left. The result of this is that, on the left-hand part, gas extraction comes back under control, but that on the right-hand part, which had originally been properly under control, more gas than necessary is now extracted. There are two disadvantages connected with this:

the first is that it adversely affects the performance of the tunnel, leading to an overconsumption of nitrogen because cold gases are extracted from the tunnel before they have had time to exchange their frigories, and

-   -   the second relates to the right-hand side of the tunnel, where         warm gases are extracted from the humid ambient air of the         space, this having the effect of creating build-ups of ice in         the extraction piping, ultimately in the medium-term blocking         them.

On the other hand, in some instances, it might be desirable to be able to have a choice of where to connect the extraction hood extraction tube, for example on one side rather than, as in the current state of the art, in the middle of the top. In practice at the present time this is not possible because connecting the extraction tube to one side of the hood immediately leads to excessive asymmetry in the extraction flow rate. The extraction flow rate is far too high on the side of the extraction tube and too low on the opposite side.

SUMMARY OF THE INVENTION

One of the objectives of the present invention is therefore to propose a technical solution to the above-mentioned problems.

As will be seen in greater detail in what follows, the present invention proposes an extraction structure the extraction cross section of which is adjustable.

The present invention effectively proposes using one or more hood(s) the extraction cross section of which can be adjusted across the width and across the depth of the conveyor belt, according to the requirements for correct operation of the tunnel, and which allows the increase or decrease in extraction flow rate to be targeted on the desired zone.

In order to do this, the proposal is to replace the usual rectangular extractor shape with an evolutionary shape, notably a triangular shape, which allows the cold gas extraction flow rate to be distributed.

Considering the above-mentioned example of gas spreading on the left-hand part of the tunnel, extraction in this zone can be increased by employing a higher speed while at the same time progressively blocking off the right-hand side so as not to affect it and so as to maintain the initial flow rate there.

The extraction flow rate across the width of the hood is thus optimized. If the left-hand part of the machine needs a higher flow rate than the right-hand part, then this system will make it possible, and this is something that is not possible with the existing technologies, to balance and adjust the extraction flow rate on the right and on the left of the machine, as required.

This “blanking-off” or “blocking-off” may be achieved for example by providing the extraction section with a movable blind or shutter, that can be actuated manually by the operator or in an automated manner, for example by reference to the measurement supplied by a sensor capable of detecting an overspill or emanation of gas at the entrance and/or at the exit of the relevant zone of the machine. This sensor may be an oxygen-content sensor or a CO₂-content sensor or else a temperature sensor or even a light beam blocked by a mist.

The present invention therefore relates to an installation for the cryogenic deep-freezing or cryogenic cooling of products, comprising a cryogenic tunnel through which the products to be deep-frozen or cooled circulate between an entrance into the tunnel and an exit from the tunnel, the tunnel being equipped with means for injecting a cryogenic fluid into the internal space of the tunnel in which the products circulate with the aid of a conveyor belt, the installation additionally comprising means for extracting the cold gases escaping from the tunnel, comprising one or more extraction hood(s), and notably an upstream first extraction hood situated facing the entrance to the tunnel and/or a downstream second extraction hood situated facing the exit from the tunnel, characterized in that the installation comprises means that make it possible to adjust the extraction cross section of at least one of said hoods across the width and over the depth of the tunnel conveyor belt.

BRIEF DESCRIPTION OF THE FIGURES

Further features and advantages of the present invention will become more clearly apparent from the following description, given by way of illustrative but nonlimiting example, with reference to the attached drawings in which:

FIG. 1 is a partial schematic view of a deep-freezing tunnel according to the prior art;

FIG. 2 and FIG. 3 illustrate embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the following elements:

the installation comprises a tunnel 1 equipped with a conveyor 2 able to transport the products that are to be treated between a tunnel entrance and a tunnel exit (the arrows 3 and 4 respectively symbolize the product entrance and exit).

the tunnel is equipped with means 5 for injecting a cryogenic fluid into the internal space of the tunnel in which the products circulate, notably here consisting of means for supplying cryogen to spray-lines for spraying the fluid into the internal space, and also comprises ventilation means 6.

in the conventional way known per se, the installation additionally comprises means for extracting the cold gases escaping from the tunnel, these means here consisting of an upstream extraction hood 7 situated facing the entrance to the tunnel and a downstream extraction hood 8 situated facing the exit from the tunnel. In this embodiment, the ducts for these two hoods 7 and 8 lead toward a common collection means 10 for collecting and discharging to the outside. However, in other embodiments currently practised, these two hood ducts discharge to the outside independently, without being collected into a common duct. Likewise, while the embodiment of FIG. 1 illustrates a configuration in which the ducts of the upstream and downstream extraction hoods are situated over the top of the conveyor, it is perfectly possible to employ a configuration in which the ducts for the upstream and/or downstream extraction hoods are situated underneath the conveyor, or some above and some below the conveyor.

FIG. 2 and FIG. 3 illustrate embodiments of the invention:

FIG. 2 illustrates, in views a) to g) thereof, various states of the cross section of a hood (viewed from beneath): not blanked off (a)) or blanked off (b) to g)), the blanking-off being achieved for example using a blind structure. The blind can open in parallel fashion from right to left, generating a rectangle (b)), the blind can also open and close in a non-parallel fashion and this then generates a structure of triangle(s) making it easier to make the distinction between the right-hand side and the left-hand side of the hood, that was desired earlier on in the present description.

and FIG. 3 illustrates the fact that, thanks to the blanking-off proposal according to the present invention, it is now conceivable to connect the extraction tube not to the middle and top of the hood, as is currently the case, but to one side of the hood, with the natural asymmetry now being able to be compensated by the system. It is therefore possible to conceive of an extraction tube connected to one of the sides (left or right) of the tunnel or even to both sides simultaneously, as illustrated in views w) and z) of FIG. 3.

As will have been appreciated from reading the foregoing, in the case of a tunnel equipped with two extraction hoods, at the entrance and at the exit, the invention makes it possible to regulate the cross section of one or each of these hoods, independently.

While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing i.e. anything else may be additionally included and remain within the scope of “comprising.” “Comprising” is defined herein as necessarily encompassing the more limited transitional terms “consisting essentially of” and “consisting of”; “comprising” may therefore be replaced by “consisting essentially of” or “consisting of” and remain within the expressly defined scope of “comprising”.

“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited. 

1-4. (canceled)
 5. An installation for the cryogenic deep-freezing or cryogenic cooling of products, comprising: a cryogenic tunnel through which the products to be deep-frozen or cooled circulate between an entrance into the tunnel and an exit from the tunnel, the tunnel being equipped with spray lines for injecting a cryogenic fluid into the internal space of the tunnel in which the products circulate with the aid of a conveyor belt; an upstream first extraction hood situated facing the entrance to the tunnel and/or a downstream second extraction hood situated facing the exit from the tunnel; and movable blinds or shutters for adjusting a cross section of at least one of said hoods across a width of the conveyor belt and over a depth of the conveyor belt by blanking off all or part of said cross section.
 6. The installation claim 5, wherein the movable shutters or blinds can be actuated in a parallel manner, generating, after blanking, a rectangle in the cross section of at least one of the hoods; and the movable shutters or blinds can be actuated in a non-parallel manner, generating, after blanking, one or two triangles in the cross section of at least one of the hoods.
 7. The installation of claim 5, wherein each hood is equipped with an extraction tube leading to the outside, connected in its middle to the top of the hood.
 8. The installation of claim 5, wherein each hood is equipped with at least one extraction tube leading to the outside, at least one of the hoods having its tube(s) connected to one side of the relevant hood. 